Comparison of two methods to determine 129I in charcoal cartridge samples by AMS

Abstract

To investigate the short- and long-term accumulated emissions from a nuclear facility, charcoal air filter cartridges were exposed at a reactor site for seven days. The short-lived 131I adsorbed in these filters was measured by gamma counting immediately after the samples were retrieved. The very long-lived 129I was analyzed later by AMS. For this purpose, two methodologies were developed: an extraction method and direct analysis, i.e., inserting an aliquot of the filter carbon directly into the target piece. The former method used a system designed to avoid sample loss resulting from the high I2 species volatility. Iodine-125 was used as a tracer to monitor the efficiency of this extraction process. The direct method was based on our experience with charcoal in the analysis of 14C in Cs sputter ion sources. In this direct analysis, charcoal samples were first spiked with a known quantity of stable iodine (127I), in an excess over the quantity naturally present in the filter, and then pressed into targets. In this way, 129I concentrations from all the charcoal samples were quickly determined. In both methods, it was found that the atom concentration of 129I in these samples exceeded that of the 131I by 2–3 orders of magnitude. These studies demonstrate the effectiveness of the charcoal capture method as a diagnostic tool for monitoring the emissions from nuclear facilities. This approach may be extended for the detection of other long-lived radioactive isotopes, which would further expand the scope of such monitoring studies.